As is well known, conventional battery-powered electric vehicles have a number of shortcomings including: the necessity of employing a plurality of large size batteries, increased weight compromising the fuel efficiency and entailing a higher production cost of the vehicles, prolonged battery charging time, low charging efficiency and relatively short battery lifespan. To overcome these problems, there have been proposed a number of power delivery systems that make use of electromagnetic induction technology.
However, there have been difficulties in applying the electromagnetic induction technology to practical use. Since motor vehicles using an energy source other than electric power also run on a public road, there are practical difficulties to construct a groove or install a rail on the road, thereby requiring the surface of the power supply coil to be flush with the road. In addition, the gap or transverse alignment between the power acquisition coil and the electric power supply coil may fluctuate with the varying weights of vehicles or rocking motions thereof.
In an effort to deal with some of the problems mentioned above, a research team of University of California at Berkeley, called PATH (Partners for Advanced Transit and Highways), has developed a power delivery system. Unfortunately, the system developed by PATH has a power transfer efficiency of about 60% even if the gap or transverse deviation between a power acquisition coil and an electric power supply coil is set to as small as 2 to 3 inches. The power supply coil has a width of about 100 cm and is buried in a road. To operate such power delivery system however, the cost required in building a road infrastructure therefor is estimated to be as high as 850,000 to 1,250,000 U.S. dollars per kilometer. Furthermore, the power delivery efficiency of 60% is too low to make the power delivery system practicable. Studies have shown that the power delivery efficiency should be at least 70% and preferably 80% or higher to be commercially viable.
In addition, there are a host of other technical problems to be resolved before a successful application of electromagnetic induction power supply technology to an actual use may be realized.
For instance, care should be taken to ensure that electric power loss attributable to magnetically induced electromotive force or electromagnetic interference does not occur when non-electric vehicles run along the road provided with such a power supply system. In case of the power delivery system developed by PATH, it has been reported that the electric power loss is 200 W/km or more on average. In order to reduce the electric power loss, therefore, it may be inevitable to drastically reduce the width of the power supply coil while increasing the frequency of the source current. Reduction in the width of the electric power supply coil poses a problem, however: for the power delivery characteristics tend to deteriorate as the transverse deviation between the power acquisition coil and the electric power supply coil becomes greater.
Furthermore, in case of the prior art electromagnetic induction-based power delivery system, it is necessary to dig a trench in the road so as to embed therein the power supply system therein including a core module, electric wires, support plate, protection cover and grounding wire, requiring the expenditure of extensive time, effort and monies. To boot, a power supply system having such a complex structure is incapable of enduring the constant running of heavy loads of vehicles thereover for an extended period of time. There may be frequent system down times occasioned by the repairing of the power supply system. Accordingly, there has existed need for an electromagnetic induction power delivery system for use in operating an electric vehicle capable of overcoming the various problems discussed above.